1. Field of the Invention.
This invention relates to protective fillers. More specifically, this invention relates to formulations which are useful as protective fillers in the splitline area of a gimbaled rocket motor.
2. Description of the Prior Art.
In a rocket motor wherein the nozzle is gimbaled to provide thrust vector control the nozzle portion of the motor is affixed to a movable housing which (when the nozzle is moved) rotates within a fixed motor housing insulation. The movable housing resembles a ball with an opening through it. Hot gases from burning propellant within the motor pass through the opening in the ball-like movable housing. Between the outer circumference of the ball-like movable housing and the inner surface of the fixed motor housing insulation is a gap of variable width. This gap is known in the art as a splitline. The splitline is necessary to allow the ball-like movable housing to rotate freely and thus permit thrust vector control.
Since hot gases from the burning propellant tend to exhaust from the rocket motor through any available opening and tend to damage the outer surface of the movable housing the splitline is packed with a filler. The filler serves two purposes. It protects the outer surface of the ball-like movable housing from the effects of heat and pressure and it, along with other suitably placed devices such as O-rings, acts to insure that exhausting gases will exhaust through the opening in the movable housing where they are supposed to.
The splitline filler then must have certain properties. It must be heat resistant. That is, it must be able to withstand the tremendous heat provided by the hot exhaust gases which it comes in contact with. Yet, it must have a low enough thermal diffusivity to insulate effectively. It must be non-abrasive. That is, since it is in contact with both the movable housing and the fixed motor insulation, its properties must be such that it does not cause friction. When it does burn, it must burn in a manner whereby no abrasive residue is left upon completion of burning. (It is permissible for a portion of the filler to burn away during flight.) And finally, it (that portion that doesn't burn away during flight) must stay in the splitline during flight. That is, its properties must be such that pressures to which it is subjected do not cause it to be mechanically removed from the splitline.
In the prior art a material known as brown zinc chromate putty (procured under military specification MIL-P-8116B) has been predominently if not exclusively used as splitline filler. Brown zinc chromate putty has a drawback in that when it burns it leaves an abrasive residue. Therefore, it is the primary objective of this invention to provide splitline filler formulations which are superior to brown zinc chromate putty. It is a further objective of this invention to provide formulations for use as protective fillers in any other situation where thermal stability and resistance to pressure are necessary.